Collisional depolarization of NO(A) by He and Ar studied by quantumbeat spectroscopy

摘要

Zeeman and hyperfine quantum beat spectroscopies have been used to measure the total elastic plusinelastic angular momentum depolarization rate constants at 300 K for NO(A 2/-9 in the presenceof He and Ar. In the case of Zeeman quantum beats it is shown how the applied magnetic field canbe used to allow measurement of depolarization rates for both angular momentum orientation andalignment. For the systems studied here, collisional loss of alignment is more efficient than loss oforientation. In the case of NO(A) with He, and to a lesser extent NO(A) with Ar, collisionaldepolarization is found to be a relatively minor process compared to rotational energy transfer,reflecting the very weak long-range forces in these systems. Detailed comparisons are made withquantum mechanical and quasiclassical trajectory calculations performed on recently developedpotential energy surfaces. For both systems, the agreement between the calculated depolarizationcross sections and the present measurements is found to be very good, suggesting that it isreasonable to consider the NO(A) bond as frozen during these angular momentum transferringcollisions. A combination of kinematic effects and differences in the potential energy surfaces areshown to be responsible for the differences observed in depolarization cross section with He and Aras a collider.